The present invention relates to a wireless communication device, non-transitory computer readable medium, and a wireless communication system. The present invention is applicable, for example, to a system in which wireless communication devices are autonomously synchronized with each other, decide communication timing, and transmit and receive data.
For example, a communication device (which will also be referred to as “node” below) included in a sensor network is configured to perform power-saving communication. Typical methods for power-saving communication include intermittently operating communication devices. For example, coordinated sampled listening (CSL) is a communication standard that adopts this intermittent operating method for communication devices (see IEEE802.15.4e).
A reception node R that performs communication in the CSL intermittently reaches a reception standby state at cycles set in advance (e.g. “reception for two milliseconds every three seconds,” etc.).
First of all, a transmission node S that performs communication in the CSL successively transmits wakeup frames for a given period in transmitting a data frame. The wakeup frame includes information indicating “how milliseconds later a data frame is to be transmitted,” or the like.
The CSL has two types of frame transmission methods: frame asynchronous transmission; and frame synchronous transmission. The frame asynchronous transmission is used when the transmission node S does not know the intermittent reception timing of the reception node R. Meanwhile, the frame synchronous transmission is used when the transmission node S knows the intermittent reception timing of the reception node R. Additionally, these two types of frame transmission method have different periods for which wakeup frames are successively transmitted.
FIG. 6 is an explanatory diagram imaging communication with the frame asynchronous transmission.
If the frame asynchronous transmission is used, the transmission node S successively transmits wakeup frames for a long period before transmitting a data frame. The wakeup frame successive transmission period lasts as long as an intermittent reception period (such as three seconds) in most cases.
FIG. 7 is an explanatory diagram imaging communication with the frame synchronous transmission.
If the frame asynchronous transmission is used, the transmission node S successively transmits wakeup frames for a short period before transmitting a data frame. The wakeup frame successive transmission period lasts as short as possible (e.g. 20 milliseconds).
Since the frame synchronous transmission has a short wakeup frame successive transmission period, overhead is low in frame transmission. However, the frame synchronous transmission has a higher probability than the frame asynchronous transmission that communication results in failure if the transmission node S falls out of synchronization with the reception node R.
The CSL standard stipulates that if no data frame arrives at a transmission destination while the frame synchronous transmission is performed (in other words, no reception response signal ACK is replied), retransmission is performed after backoff and carrier sense as in normal data communication.
If the transmission node S receives a reception response signal ACK from the reception node R and further transmits data frames with some frequency, the transmission node S rarely falls out of synchronization with the reception node R.
This is because a reception response signal ACK includes intermittent reception timing information (more specifically, an intermittent reception cycle and a phase in reception of a data frame) on the reception node R in the CSL, and the transmission node S can compute the intermittent reception timing of the reception node R again on the basis of the information every time the transmission node S transmits a frame.